[libvirt] libvirt/kvm config for routed networking

[Daniel P. Berrange]

On Thu, Oct 08, 2009 at 09:44:45AM +0100, William Wagner wrote:
> Hello,
> 
> I hope this is the right list I should post to as my question is not 
> development related.
> 
> I am trying to setup a kvm/libvirt VM on my host (Ubuntu jaunty). My 
> host has a public static IP and my VM also has a public static IP. 
> Unfortunately I can not use bridged networking as the hosting provider 
> has configured their switch to only accept packets from the MAC address 
> of the host.
> 
> I want to be able to setup my VM so it has the public static IP and it 
> appears to be directly connected to the net. I believe I can do this 
> with routed networking.
> 
> I have created a new routed network:
> <network>
> <name>routed-net</name>
> <bridge name="routed%d" />
> <forward mode="route" dev="eth0"/>
> <ip address="10.255.255.2" netmask="255.255.255.255">
> </ip>
> </network>
> 
> and in my vm's config I have:
> <interface type='user'>

That should be type='network' if you want the VM to associate
with the network you defined above.

> <source network='routed-net'/>
> <mac address='54:52:00:47:a8:38'/>
> <model type='virtio'/>
> </interface>
> 
> Will this mean that the VM is placed on the routed network?
> 
> Then I just need to add suitable routing rules on the host and 
> everything should work?

In theory yes, but I'm afraid I've never tried this type of config
myself.

> Is there a way to get libvirt to add the rules automatically when the VM 
> starts. I have previously used Xen where you are able to specify what 
> the IP address of the VM is and entries are automatically added to 
> iptables. Is there similar syntax for libvirt and if so what is it? If 
> not how do you recommend adding the routing rules?

If using type='network' then the idea is that things are all done for
you automatically. If you want todo the xen style approach manually,
then you can use type='ethernet' and use the <script> element to 
point to a shell script for configuring the VM - the script would do
just the same kind of thing that would have done on Xen. We don't
particularly recommend type=ethernet as a general rule, but it is a
useful generic catch-all fallback for unusual scenarios like yours


Daniel
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